The general objectives of these studies are to detail the physiological and genetic bases for the pathogenicity of selected oral microbes. Present studies are focused on the following topics: 1) Mutants of Streptococcus mutans with altered sucrose-metabolizing enzymes. 2) Control of glucosyl transferase and plaque formation by S. mutans in nutrient-limited continuous cultures. 3) Possible role of extracellular glucosyl transferase from Streptococcus salivarius in plaque formation.